Characterising satellite aerodynamics in Very Low Earth Orbit inclusive of ion thruster plume-thermosphere/ionosphere interactions

This work presents particle-based kinetic simulations of ion thruster plasma plumes, in an analysis of the modified spacecraft charged drag profile, resultant of plume interactions with the ambient thermosphere/ionosphere in Very Low Earth Orbit (VLEO). VLEO is a highly appealing region for spacecraft operations, as it offers high-performing economical spacecraft platforms, but the mission lifetime is very limited owing to high drag from the residual atmosphere. Detailed characterisation of plume dynamics is vital in exploring the feasibility of Electric Propulsion (EP) as a means of continuous drag compensation at such altitudes. Quasi-neutral Direct Simulation Monte-Carlo – Particle-in-Cell simulations, involving interactions of ion thruster plumes with rarefied ambient thermosphere/ionosphere, are presented for steady drag-compensating thruster firings in orbits of 150 and 400 km. It is shown that the flow profile is affected by a combination of collisional and indirect electrostatic field mechanisms. In the immediate aft region of the spacecraft, the interaction is driven by pick-up of freestream ions within the charge-exchange cloud. The main effect of the plume is to simply deflect the freestream, as ionosphere particles collide with primary beam propellant, and the freestream number density increases at the spacecraft trailing edge as particles are captured at the charge-exchange cloud. The consequences of the observed mechanisms on the spacecraft drag are theorised, and it is shown that effects of EP plume plasma in VLEO should be included in future analyses, to ensure drag models are complete.